Heterocyclic dye sensitised electrophotographic material

ABSTRACT

The sensitization of layers containing a photoconductor by the inclusion of a heterocyclic dye compound characterized in that the sensitization is increased while the product exhibits longevity.

United States Patent [191 Riester et a1.

HETEROCYCLIC DYE SENSITISED ELECTROPHOTOGRAPHIC MATERIAL Inventors: Oskar Riester, Leverkusen; Wolf Gesierich, Opladen-Grosserdriesch,

both of Germany AGFA-Gevaert Aktiengesellschaft, Leverkusen, Germany Filed: Aug. 9, 1972 Appl. No.: 279,251

Related U.S. Application Data Continuation of Ser. No. 34,626, May 4, 1970, abandoned, which is a continuation of Ser. No. $71,244, Aug. 9, 1966, abandoned.

Assignee:

Foreign Application Priority Data Oct. 15, 1965 Germany 50509 U.S. Cl. 96/1.7, 96/1.6

Int. Cl. G03g 5/08, G03g 5/00, G03g 7/00 Field of Search 96/1.6, 1.7, 120, 139;

[56] References Cited UNITED STATES PATENTS 2,332,517 10/1943 Kendall 260/240 3,114,633 12/1963 Schlesinger 3,287,123 11/1966 Hoegl 3,352,670 11/1969 Coles 96/l.7

FOREIGN PATENTS OR APPLICATIONS 41-12991 7/1966 Japan 96/1.7

Primary Examiner-Charles L. Bowers, Jr. Attorney, Agent, or Firm-Connolly and l-lutz [57] ABSTRACT The sensitization of layers containing a photoconductor by the inclusion of a heterocyclic dye compound characterized in that the sensitization is increased while the product exhibits longevity.

. China. 7 D ingF mmm m4 3344.782

FIG 6 FIG. 7-

- INVENTORS. OSKAR RIESTER, WOLF GES/ER/CH.

BY v a @kw HETEROCYCLIC DYE SENSITISED ELECTROPHOTOGRAPHI C MATERIAL This application is a continuation-of applicants copending application Ser. No. 34,626, filed May 4, i970, which is a continuation of US. application Ser.

No. 57l ,244,filed Aug. 9, i966, both now abandoned.

it is already known that when the intrinsic sensitivity ofphotoconductive layers lies substantially in the ultraviolet region of the spectruin the layers can be sensitised to visible light by the addition of dyes which trans-.

fer radiant energy. The dyes which have been proposed for this purpose belong to a variety of different classes of compounds, e.g. triphenyl methane dyes, phenol sulphonphthaleins, xanthene and acridine dyes as well as cyanines and merocyanines, which exemplify the class of polymethine dyes, and oxonoles.

The foregoing dyes, however, suffer the disadvantage that they either do not provide sufficient increase in sensitivity or they add too much colour to the electrophotographic layer. As a rule, only colourless or almost colourless layers are desired. This detrimental discoloration is particularly serious in the case of electrophotographic materials since the sensitising dyes used are not washed out during the usual working up methods, or are not destroyed in the baths. To bleach out the sensitising dyes after the photograph is completed is usually too complicated.

The object of the present invention is to provide a method for optically developing sensitised electrophotographic layers which preferably contain zinc oxide as 'photoco'nducter and which are as far as possible, colo'ur'less and are stable on storage, especially in respect of their sensitivity. It has now been found that very good sensitisation in the blue-violet region of the spectrum can ben achieved by the use of methylene dithiocarboxylic acid esters of heterocyclic compounds.

The desired compounds have the following general formula wherein Z is a sulphur or selenium atom Or a group, Y is a --N= atom or a 5 CR group, R is (1) an alkyl or alkenyl group preferably having I to 6 C- ator'ns, such as methyl, ethyl or propyl, and the alkyl radical may be substituted e.g. by a halogen atom such as chlorine or bromine, or a hydroxyl, carboxyl, carbalkoxy; sulpho or sulphato group, (2) a cycloalkyl group such as cyclohexyl, (3) or aryl group such as phenyl or naphthyl or (4) an aralkyl group such as benzyl or phenylethyl; R" is (l) a hydrogen atom (2) an alkyl or alkenyl group having preferably 1 to 6 C- atoms, which may be substituted by a hydroxyl, alkoxy, or phenyl group, (3) a cycloalkyl group such as cyclohexyl or (4) an aryl groupsuch as phenyl or naphthyl; R and R" may together denote the ring members required for completing a 5- or 6-membered heterocyclic ring; R' is l) a hydrogen atom, (2) an alkyl or alkenyl group having preferably 1 to 6 C-atoms, which may be substituted by a phenyl, carbamyl, acylamino, carbalkoxy group and the like, (3) a cycloalkyl group such as cyclohexyl, (4) an aryl group such as phenyl or naphthyl or (5) an acyl, acylamino, carboxy, or carboxyester group; R' has the same meaning as R', or together'with R' forms the ring members required for completing a fused carbocyclic ring; R is a hydrogen atom or an alkyl group having preferably up to 5 C- ato'ms and X has the same meaning as R or is hydrogen or a group of the following formula:

6,7-tetramethylenebenzthiazole, those of the selenazole series such as benzoselenazole or those of the indoline series such as 1,3,3-trimethylindoline, 5- methoxyl ,3 ,3-trimethylindoline.

The following compounds have proved to be particularly advantageous:

(I) /S\ s H o=o-c isom II s S 1| o=o-o-som i CH3 (III) s\ s 'H /o=o-ii-somomomsoafi \N (IV) s\ s s /s\ /c=c- H -s-s-d-o=c\ \III I rHa CrHs S03 S039 XII XIV

| (CH2)3SOsK The preparation of the compounds used as sensitizing dyes according to this invention is already known.

The compounds to be used according to the invention are prepared by known methods, eg from heterocyclic quaternary salts which are substituted by a methylene group in the N-Z-position by the addition of carbon disulphide and csterification of of the resulting terminal dithiocarboxylic acids.

Reference is made to US. Pat. No. 2,332,517 issued Oct. 26, 1943 and preparation of the dithiocarboxylic acid can be effected, for example, by the process described as follows. A quaternary salt of a'heterocyclic nitrogen compound containing a reactive methyl or mono-substituted methyl group in the a or 7 position to the heterocyclic quaternary nitrogen atom, is reacted with a compound of the following formula:

where the groups R are hydrocarbon residues, as for example alkyl, aryl or aralkyl groups and said com- LII pound being present in an excess of over one molecular equivalent of the quaternary salt. The reaction takes place in a solvent in the presence of a base. The following reaction is indicated as taking place:

D represents components to complete the heterocyclic nitrogen compound,

R represents an alkyl or aralkyl group,

R represents hydrogen or an alkyl, aryl or aralkyl group,

R represents an alkyl, aryl or aralkyl group,

X represents an acid residue.

n 0 or 1.

This reaction may involve any of known type of heterocyclic quaternary ammonium compounds containing the specified reactive methyl group known for use in the manufacture of cyanine-dyes, as for example the substituted and unsubstituted thiazoles, oxazolcs, selenazoles and their polycyclic homologues such those of the benzene, naphthalene, acenaphthene and anthracene series; pyridine and its polycyclic homologues such as quinoline and a and y naphthaquinolines; lepidines; indolenines; diazines; such as pyrimidines and quinazolines; diazoles (e.g. thio-BB'-diazole); oxazolines, thiazolines and selenazolines. The polycyclic compounds of these series may also be'substituted in. the carbocyclic rings with one or more groups such as alkyl, aryl, amino, hydroxy, alkoxy and methylene dioxy groups, or by halogen atoms.

In the foregoing formulae the groups R, R and R may be alkyl groups and examples are the methyl, ethyl, propyl and higher alkyl groups, allyl and similar unsubstituted groups, or they may be aralkyl groups,

e.g. benzyl group; R and R may be an aryl group, e.g.

phenyl or naphthyl groups.

While the reaction may take place by heating the reagents together in the presence of a base and a solvent, it is preferred to carry on the reaction in the presence of an excess of a strong base.

This process produces a dithiocarboxylic acid which may be used for the production of the sensitizing dye.

The dyes according to the invention can be used to sensitise an electrophotographic layer, in particular a zinc oxide layer, in the blue region of the spectrum with sensitation maxima of 420 to 460 mu. These dyes have a characteristically narrow sensitisation range with steep drop of the sensitisation curve towards the long wave region of the spectrum and have high sensitisation intensity. This makes them eminently suitable for blue sensitisation of electrophotographic materials such as for example, colour materials which are processed with copying light containing a high proportion of blue light. Another advantage of the dyes according to the invention is that discoloration of the photographic layers is almost imperceptible.

The sensitisers according to the invention are added to the layers in such quantitiesthat about 0.1 to l mg of sensitiser are present per square metre of completed photoconductive layer.

Sensitisation of electrophotographic layers is usually carried out by triturating the photoconductive pigment with the solution of the sensitising dye in a suitable solvent such as methyl or ethyl alcohol and evaporating off the solvent. The sensitising dye precipitates on the surface of the grain of the photoconductive pigment when this operation is carried out. The pigment can now be worked up with a dilute solution of a lacquer binder to produce the electrophotographic layer. The dye according to the invention may equally well be used in other sensitisation methods. In one of these processes, for example, the solution of sensitising dye in a liquid which is inert to the binder is added to the mixture of photoconductor and binder before dispersion. Another possible method, is the sensitisation process described in British Patent Specification 919,684 which has the advantage of providing electrophotographic layers with only slight discoloration. Finally, the sensitivity of a completed layer of photoconductor and binder which has not been sensitised can be shifted into the region of the visible spectrum of longer wave length by subsequent immersion in a solution of the sensitising dye followed by drying. Hence, it will be clear from this that the use of the sensitising dye according to the invention is not limited to any particular working up process.

Furthermore, the use of the dye according to the in vention is not limited to any particular types of photoconductors and binders. Compounds which can be used as photoconductors in such systems are, in particular, inorganic and organic compounds which by virtue of their own colour do not already have a sensitivity maximum in the sensitising region of the dyes according to the invention. Examples of suitable compounds are zinc oxide, titanium dioxide or arsenious trioxide or organic compounds such as anthracene or phenanthrene. Any of the film-forming agents customarily used in electrophotography, such as silicone resins, alkyd resins, polyurethanes on polyvinyl acetate, can be used as binders for the layers sensitized according to the present invention.

EXAMPLE:

10 mg of dye No. III are dissolved in ml methyl alcohol. The solution is added to 100 g of a photoconductive zinc oxide and intimately mixed with the powder. The solvent is then removed by evaporation at 65C. To prepare the electrophotographic layer, the zinc oxide which has now been coloured is dispersed in a mixing apparatus with 45 ml of a 60 percent solution of a phenyl-methylpoly-silicone resin in toluene, another l00 ml toluene is added to the mixture and it is then applied to a baryted paper support and dried. The electrophotographic material thus obtained is exposed to form an image after it has been charged and is then developed by one of the usual development processes with the use of a toning powder or a liquid aerosol. Excellent reproduction of the original is obtained.

Similarly good results are obtained if instead of dye No. III, one of the following dyes is used: XII, IV, XIV, V and XV.

The spectral sensitivity of the zinc oxide layers prepared according to the above examples is showed in the attached FIGS. 1 to 7. FIG. 1 show the spectral sensitivity curve of a zinc oxide layer which has not been sensitised, FIG. 2 the sensitisation properties of the material prepared according to the Example, and FIGS. 3 to 7 the photoconductive Layers obtained with the use of dyes No. XII (FIG. 3), No. lV (FIG. 4), No. XIV (FIG. 5), No. V (FIG. 6), No. XV (FIG. 7).

The sensitisation curves are obtained as follows:

The layer which is to to be examined, in contact with an interference graduated line filter VERIL B-60 made by Schott & Genossen is exposed to 4,000 Lux seconds of an image enlarging lamp RADIUM R 226 (230 V/250 W). During this operation, the filter is covered with a transparent grey step wedge so that a curve is obtained on the photoconductive layer typical of the image which is capable of being developed, which curve is shown as a line drawing in the appended figures. The effectiveness of the sensitising dye can be assessed by the height of the ordinate at its maximum on this sensitisation curve, whilst the position of the sensitisation maximum in the visible region of the spectrum can be determined from the abscissa.

The eIectro-aerosol process described in British Patent Speciflcation 994,645 was used in all cases to render the filter exposure visible.

The photoconductive material according to the invention can be used for all electrophotographic processes, for example for development processes which make use of a solid pulverulent toning powder, for aerosol development processes electrophoretic processes and so-called wetting development processes. The materials according to the invention are suitable both for electrostatic charge images and for conductive images.

We claim: -1. Photosensitive electrophotographic material having a layer of photoconductive material comprised of said dye being present in the amount of 0.1 to 10 mg. per square meter of the photoconductive layer.

2. Photosensitive electrophotographic material according to claim 1 in which the dye is a benzthiazole compound.

3. Photosensitive electrophotographic material according to claim 1 in which the photoconductive material is zinc oxide dispersed in a hinder. 

1. PHOTOSENSITIVE ELECTROPHOTOGRAPHIC MATERIAL HAVING A LAYER OF PHOTOCONDUCTIVE MATERIAL COMPRISED OF ZINC OXIDE SENSITIZED BY A METHYLENE DITHIOCARBOXYLIC ACID ESTER OF A HETEROCYCLIC COMPOUND DYE OF HE FORMULA
 2. Photosensitive electrophotographic material according to claim 1 in which the dye is a benzthiazole compound.
 3. Photosensitive electrophotographic material according to claim 1 in which the photoconductive material is zinc oxide dispersed in a binder. 